1. Field of the Invention
This invention relates to a new process for the production of polymer dispersions of low surface tension. The process of the invention utilizes a mixed emulsifier of .alpha.-sulfocarboxylic acids and esters thereof.
2. Description of the Relevant Art
Emulsion polymerization processes in which .alpha.-sulfofatty acids or esters thereof with lower alcohols are used as emulsifiers are already known. Thus, U.S. Pat. No. 2,694,052 describes the use of sulfonated and sulfated fatty acid esters in the homopolymerization of vinyl acetate in the presence of molecular weight regulators and inorganic cyanides. Although stable polymer dispersions (emulsions) are obtained in this process, there is nothing in this U.S. patent to suggest that a wide range of applications are possible for mixed emulsifiers of .alpha.-sulfocarboxylic acids and their esters.
The use of sulfofatty acids containing less than 10 carbon atoms in an emulsion polymerization process for the production of PVC is described in German Pat. No. 842 119. According to the teachings of this German patent, however, only coarsely dispersed suspensions are obtained. There is no reference therein to the use of a combination of the acids with their esters. German Applications No. 17 20 430 and No. 19 01 493, both of which relate to processes for the production of PVC in the presence of .alpha.-sulfofatty acids, do not suggest any advantage for using .alpha.-sulfocarboxylic acids in combination with their esters.
Finally, German Application No. 20 15 660 relates to a process for the production of speck-free, hot-polymerized plastics dispersions of high surface tension, in which .alpha.-sulfofatty acids or .alpha.-sulfofatty acid esters each containing from 10 to 20 carbon atoms in the acid residue and up to 3 carbon atoms in the alcohol residue are used as the polymerization emulsifier. Although .alpha.-sulfocarboxylic acids and also their esters are mentioned as polymerization emulsifiers in this German Application, their combined use is neither described nor suggested. This is also apparent from the fact that while it has now surprisingly been found that the combined use of .alpha.-sulfocarboxylic acids and their esters in the emulsion polymerization process leads to dispersions of low surface tension, while the use of the individual components according to the prior art leads to dispersions of high surface tension. There is also nothing in this German Application to suggest other advantages of using the emulsifier combination, which have been discovered by the present invention, such as for example improved stability in storage.